The present invention relates to a valve for fluid flow and, in particular, to an injector valve for boosting air flow and air pressure in a pneumatic conveyor system.
Pneumatic conveyors are often employed for a wide variety of applications, including the transfer of dry granular materials such as sand, salt, grain, flour and cement. Two types of systems are generally used for the transfer of granular materials. They are "dilute phase" systems and "dense phase" systems.
A dilute phase system depends upon a high velocity air stream to carry a relatively small amount of material at high speeds. Serious disadvantages often accompany this method. The high speed of the particles also tends to abrade the interior surfaces of the conveyor tubes and other equipment. Hence, maintenance is often a necessity and frequent operational shut-downs are often required to repair and replace parts. In addition, the high velocity impacts which are unavoidable in this type of system tend to destroy the transported material by reducing it to an undesirably low grain size, thereby causing the formation of fines and dust.
A preferred type of pneumatic conveyor which avoids many of these problems is the dense phase system. This is a slow speed system in which the conveyor tube is practically full of particulate material and the material is moved by air pressure applied to it at its source and at a number of successive locations along the conveyor tube. Although the speed of the material is less, the density is so much higher that the net volume of material moved per unit of time is usually much higher than in the high speed dilute phase system. Furthermore, wear is reduced on the conveyor tube and the material being transported is usually damaged to a lesser degree.
The present invention relates to the injector valves or booster valves which are positioned along the conveyor tube of a dense phase system. Some prior art injector valves are extremely difficult to adjust. If too much pressure is applied, the material in the conveyor is blocked. On the other hand, if the pressure is too low, the material is not properly transported. Since the proper applied pressure depends upon the pressure inside the conveyor tube, and since the pressure in the tube varies with the material density, flow rate, consistency, and the pressure applied by adjacent injector valves, it is readily apparent that it is often difficult to achieve the correct pressure. Continual adjustments are often necessary to maintain the careful balance of the system.
One method of simplifying this type of pneumatic conveyor system is to employ one-way valves in the booster stations which operate to release pressurized gas into the conveyor tube when the pressure in the tube drops below a predetermined value. However, these valves often become clogged due to particulate material in the conduit leading from the one-way booster valve to the conveyor tube backing up into the valve before it can close. The backed up particulate matter soon scores the sealing surfaces of the valve and valve replacement becomes necessary.
Accordingly, it is an object of the present invention to provide an improved injector valve for adding pneumatic pressure or gas flow, as required, in order to keep particulate matter moving steadily through a pneumatic conveyor tube.
It is another object of the present invention to provide an improved one-way injector valve for a booster station which operates to release pressurized gas into the pneumatic conveyor tube when the pressure in the conveyor tube drops below a predetermined level.
It is another object of the present invention to provide an improved injector valve which does not experience the clogging that is commonly caused by conveyed particulate matter backing into the valve before it can close.